Sterlinghillite

Chemical formula: Mn₂+₃(As₅+O₄)₂·₃H₂O

A rare, secondary manganese arsenate with an intense pink color, known exclusively from the Sterling Mine in New Jersey, USA.

## Characteristics Sterlinghillite is a hydrated manganese arsenate, forming small but visually striking aggregates. It most commonly occurs as microscopic, radial aggregates or rosettes composed of acicular and bladed crystals. Individual crystals rarely exceed 1 mm in length. Due to its intense pink to reddish-pink color, it is easily noticeable against the darker host rock. ## Physical Properties Sterlinghillite crystals exhibit a vitreous to pearly luster, especially on cleavage surfaces. The mineral is translucent. Its Mohs hardness is approximately 3, making it relatively soft and susceptible to scratching. It is a brittle mineral. ## Colors and Varieties Sterlinghillite is prized for its characteristic, vivid color, which ranges from light pink, through intense pink, to reddish-pink. No distinct varieties have been identified. ## History and Name The mineral was first described in 1981 by Pete J. Dunn, Donald R. Peacor, and Nels E. Leavens. Its name comes from its discovery locality – the famous Sterling Hill Mine in Ogdensburg, Sussex County, New Jersey, USA, which is its type locality and the only known occurrence. ## Uses Sterlinghillite has no industrial applications. It is exclusively a valued and sought-after collector's mineral due to its rarity, attractive appearance, and origin from a classic, historic locality.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Pale pink
Density: 3.61
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of sterlinghillite include its intense pink color, radial aggregates of small, acicular crystals, and occurrence in association with minerals from the Franklin-Sterling Hill deposit. Reaction to UV light is not a diagnostic feature. ## Distinguishing from Similar Minerals Sterlinghillite can be confused with other pink arsenates from the brandtite group, such as brandtite or talmessite, which may also occur at Sterling Hill. Final differentiation requires advanced analytical methods (e.g., XRD). It is distinguished from pink rhodochrosite by its crystal habit (acicular vs. rhombohedral) and the harder host rock (franklinite, willemite) in which it occurs. ## Crystal Forms The mineral forms radial aggregates, rosettes, and fan-shaped clusters. These consist of small, elongated, bladed or acicular crystals that are flattened along one axis.

Geological environment

## Genesis Sterlinghillite is a secondary mineral. It forms in the oxidation zone of metamorphosed zinc, manganese, and iron ore deposits. It crystallizes in fractures and small rock cavities as a result of low-temperature hydrothermal processes acting on earlier arsenic minerals. ## Mineral Associations This mineral occurs in association with other rare minerals characteristic of the Sterling Hill deposit. It most commonly co-occurs with willemite, franklinite, calcite, andradite, as well as other arsenates such as kottigite, parasymplesite, and brandtite. ## Localities The only confirmed occurrence of sterlinghillite in the world is its type locality: the Sterling Hill Mine in Ogdensburg, Sussex County, New Jersey, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most prized sterlinghillite specimens are those with rich, dense clusters of radial aggregates with an intense, deep pink color. Strong contrast with the dark host rock (most often franklinite) is highly valued. The size and aesthetics of the rosettes, as well as the absence of damage to delicate crystals, significantly increase the specimen's collectible value. ## Popular Localities The only source of sterlinghillite specimens is the historic Sterling Hill Mine in New Jersey, USA. All minerals available on the collector's market originate from this single location.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Contact with water, especially for extended periods, is not recommended due to the risk of damaging delicate crystals and potential chemical reaction. If liquid is necessary, only isopropyl alcohol should be used and dried immediately. ## What to Avoid Avoid ultrasonic cleaners, washing in water, acids, and all chemical agents. The mineral is soft and brittle, so it must be protected from impacts, scratching, and vibrations. As an arsenate, it is toxic – avoid inhaling dust and wash hands after each contact. ## Storage It is recommended to store specimens in closed, stable containers (e.g., perky boxes) to protect them from dust, mechanical damage, and sudden changes in humidity. Keep it away from children and pets.

Sources

IMA Mineral List (CNMNC)